Re: [RFC 5/5] USB: Eliminate delays involved in root hub initialization during HNP

[Pavan Kondeti <pkondeti@codeaurora.org>]

On 12/15/2010 5:51 PM, Felipe Balbi wrote:
> On Wed, Dec 15, 2010 at 04:44:14PM +0530, Pavankumar Kondeti wrote:
>> Some USB controllers have common resources (IRQ, register address
>> space) for Host, Peripheral and OTG.  So HCD is added only before
>> entering into Host mode.  Root hub initialization is done in
>> different steps to decrease boot up time.  But this makes B-device
>> difficult to meet HNP timings.  Hence eliminate delays involved in
>> root hub initialization for B-host.
> 
> I wonder if this is the best approach. Would it be easier to not touch
> usbcore, probe the entire stack during boot but have a "core" layer
> handling synchronization to shared resources ?
> 
The implementation is like this:

Actually OTG synchronizes UDC and HCD. OTG driver probe will be called
first and it takes care of turning on clocks, resetting controller and
PHY and enabling interrupts (VBUS and Id). UDC and HCD will not modify
hardware registers in their probe functions. So HCD will not call
usb_add_hcd() function in it's probe(). After HCD and UDC registers with
OTG via otg_set_xxx(), OTG activates HCD (by calling usb_add_hcd()) or
UDC (usb_gadget_connect()) based on Id/VBUS status. When gadget is
active, HCD is detached from USB core (usb_remove_hcd()). So user space
can not poke into sysfs/debugfs nodes provided in the usb core.

> Maybe you could make your device an MFD device that allocates
> platform_devices for its children (HCI, UDC, OTG, etc) and pass in a
> bunch of read/write functions as platform_data for them to use as
> accessors to shared register space ?!? Would that work ?
> 
The easy way to deal this problem is removing HCD when Mini/Micro -A
cable is detached.

This patch addresses the issues (usb_add_hcd() taking too much time
)when B-peripheral becomes B-host.

>> This patch also marks hnp_supported flag TURE for B-host while
> 
> s/TURE/TRUE
> 
Fixed in V2.

Thanks,
Pavan

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